<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="https://cdn.bootcss.com/jquery/1.11.3/jquery.js"></script>
</head>
<body>

<input type="text" name="testtest"/>
<select name="test" id="select_id">
    <option value="1" data-value="12" selected>10</option>
    <option value="2" data-value="22">20</option>
    <option value="value">value</option>
</select>

<script>

    $(function () {
        var a = $("select[name='test']").find("option:selected").text();  //建议
         $("input[name='test']").find("option:selected").text();
        console.log(a);
        $("input[name='testtest']").val(11);
    })
</script>
</body>
</html>